To explore the value of metagenomic next-generation sequencing (mNGS) technology in the etiological diagnosis of sepsis in preterm infants following antibiotic use. A retrospective analysis of medical records for 45 preterm infants with sepsis who were treated at Henan Provincial People's Hospital. All patients received antibiotic treatment for ≥3 days and underwent both blood culture and mNGS testing. The detection rates of pathogens by blood culture and mNGS testing were compared. The positive detection rate of pathogens by blood mNGS was higher than that by blood culture (44% vs 4%; P<0.001). Blood mNGS detected 28 strains of pathogens, including 23 bacteria, 4 fungi, and 1 Ureaplasma parvum. Blood culture identified one case each of Rhodotorula mucilaginosa and Klebsiella pneumoniae. In the group treated with antibiotics for >10 days, the positive rate of blood mNGS testing was higher than that of blood culture (40% vs 3%; P<0.001); similarly, in the group treated with antibiotics for ≤10 days, the positive rate of blood mNGS testing was also higher than that of blood culture (53% vs 7%; P=0.020). Treatment plans were adjusted based on blood mNGS results for 13 patients, with an effectiveness rate of 85% (11/13). In preterm infants with sepsis following antibiotic use, the positive rate of pathogen detection by blood mNGS is higher than that by blood culture and is unaffected by the duration of antibiotic use. Therefore, mNGS testing can be considered for confirming pathogens when clinical suspicion of infection is high but blood culture fails to detect the pathogen.